Selective preparation of some 2-alkoxy-ethanol derivatives

ABSTRACT

A method for producing certain 2-alkoxy-ethanol derivatives by depolymerising oligomeric or polymeric polyglycol derivatives in the presence of alcoholate or 1,3-diketonate derivatives of zirconium, titanium, aluminum or molybdenum.

This application is a 371 filing of International Patent Application PCT/IB2008/053617, filed Sep. 8, 2008.

TECHNICAL FIELD

The present invention relates to the field of organic chemistry and more specifically to a method for producing some 2-alkoxy-ethanol derivatives. The present method comprises the steps of depolymerising some oligomeric or polymeric polyglycol derivatives in the presence of alcoholate 1,3-diketonate derivatives of zirconium, titanium, aluminium or molybdenum.

PRIOR ART

The simplest way to produce 2-alkoxy-ethanol derivatives comprises the addition of an alcohol to an epoxide to obtain a 1/1 adduct (i.e. the desired product). However this method gives, in the vast majority of cases, a number of oligomeric or polymeric by-products (i.e. 2-alkoxy-polyethyleneglycol derivatives). These by-products are undesirable and are a lost of precious starting alcohol. Furthermore, said method implies working conditions necessitating low conversations in order to minimize the formation of said by-products and the lost of the starting alcohol.

In order to recycle the undesired by products mentioned above, in the prior art there are reported a number of methods (e.g. treatment by strong protic acids) which allow only the conversion of a 2-alkoxy-polyethyleneglycol derivative directly to the free starting alcohol (for instance see U.S. Pat. No. 5,770,678). This solution is not satisfactory for obvious reasons.

To the best of our knowledge, in the prior art there is only one document suggesting that a selective conversion (i.e. that stops exactly at the desired product: the 1/1 adduct) of a 2-alkoxy-polyethyleneglycol derivative can be performed (FR 2447363). However this document discloses hydrogenation conditions requiring very strong temperatures (e.g. 250° C.) where a very limited number of substrates can survive.

Therefore there is still a need for a process allowing carrying out the invention's process under milder conditions.

DESCRIPTION OF THE INVENTION

We have discovered that some 2-alkoxy-ethanols can be selectively produced by treating a polyethylene glycol derivative with a particular type of zirconium complex.

Therefore, an aspect of the present invention concerns a process for producing a compound of formula

wherein z represents 1 or 0, and each R¹, independently from each other, represents a hydrogen atom or a methyl or ethyl group, or the two R¹ taken together represent a (CH₂)_(m) group, m representing 3, 4, or 5; each R², independently from each other, represents a hydrogen atom or a methyl or ethyl group, or the two R² taken together represent a (CH₂)_(m) group, m representing 3, 4, or 5; and R³ represents a phenyl group optionally substituted, a saturated or unsaturated C₅-C₆ cyclic hydrocarbon moiety optionally substituted, or a CH(R⁴)₂ or R⁴CH═CR⁴ moiety, R⁴ representing a C₁-C₆ alkyl or alkenyl group optionally substituted; said process comprising the step of reacting the corresponding compound of formula

wherein z, R¹, R² and R³ are defined as in formula (I) and x represents an integer comprised between 2 and 10; with at least one metal compound of formula M(R⁵)_((n-2y))(R⁶)_(y), wherein y is 0, 1 or 2; M representing Zr or Ti, and n is 4, or Al and n is 3, or Mo(O₂)₂ and n is 2; R⁵ representing, independently from each other, a C₁-C₆ alkoxylate group or a C₅-C₈ 1,3-diketonate, and R⁶ representing a 1,2- or 1,3-dialkoxylate or a 1,2-diphenoxylate.

According to a particular embodiment of the invention, the compounds of formula (I) are those wherein z represents 1,

each R¹, independently from each other, represents a hydrogen atom or a methyl group, or the two R¹ taken together represent a (CH₂)_(m) group, m representing 3 or 4;

each R², independently from each other, represents a hydrogen atom or a methyl group, or the two R² taken together represent a (CH₂)_(m) group, m representing 3 or 4; and

R³ represents a saturated or unsaturated C₅-C₆ cyclic hydrocarbon moiety optionally substituted, or a CH(R⁴)₂ or R⁴CH═CR⁴ moiety, R⁴ representing a C₁-C₄ alkyl group optionally substituted.

According to an embodiment of the invention, the corresponding compound of formula (II) can be one wherein x represents an integer comprised between 2 and 5.

In all the embodiments of the invention, optional substituents of R³ are one, two or three C₁-C₃ alkyl, alkenyl or alkoxy groups, for example methyl or ethyl.

As non-limiting typical examples of R³ groups one may cite the following: 3,3-dimethyl-cyclohexyl, 3,3-dimethyl-cyclohex-1-en-1-yl, 4-methyl-pent-2-en-2-yl, 5-methyl-cyclohex-3-en-1-yl, 2-methyl-cyclohexyl.

According to a particular embodiment, one or two R¹, per glycol unit of compound (I) or (II), are a methyl group. Similarly, at least one R² is a methyl group.

The starting compound (II) can be simply prepared by adding an alcohol of formula R³(R²)₂COH to an excess of the epoxide (C(R¹)₂CH₂))O under conditions well known by a person skilled in the art.

The invention's process allows the preparation of the desired 2-alkoxy-ethanol without being impeded by the need of low conversions conditions to avoid the formation of polymeric products, and therefore the overall yield and global productivity is improved.

As previously mentioned, the use of a metal compound as described above allows a selective conversion of the poly-glycolic chain of (II) into the corresponding compound (I), which is the equivalent of a selective 1/1 addition on an alcohol to an epoxide, i.e. the alcohol R³(R²)₂COH is not the main product.

In particular the metal compound can be one of formula M(R⁵)_((n-2y))(R⁶)_(y), wherein y is 0 or 1; M representing Zr or Ti, and n is 4, or Al and n is 3; R⁵ representing, independently from each other, a C₁-C₆ alkoxylate group or a C₅-C₈ 1,3-diketonate; and R⁶ representing a 1,2- or 1,3-dialkoxylate.

According to a particular embodiment of the invention, said metal compound can be a compound of formula M(R⁵)₄, M being Zr or Ti, or of formula Al(R⁵)₃, R⁵ having the meaning described above.

According to a particular embodiment of the invention, said metal compound can be one of formula Zr(R⁵)₄ or Al(R⁵)₃, R⁵ having the meaning described above.

According to any one of the above embodiments, all R⁵ groups represent an alkoxylate group or a 1,3-diketonate group.

According to any one of the above embodiments, the R⁵ group is ⁻OMe, ⁻OEt, ⁻OPr, ⁻O^(i)Pr, BuO, ^(t)BuO or acetylacetonate, in particular OPr, ⁻O^(i)Pr, BuO, ^(t)BuO or acetylacetonate.

According to a particular embodiment of the invention, the R⁶ group is ⁻OCH₂CH₂O⁻.

The metal compounds are known compounds and the methods for their preparation is well known in the literature.

Useful quantities of metal compound, added to the reaction mixture, may be comprised in a relatively large range. One can cite, as non-limiting examples, ranges between 0.005 and 1 molar equivalents, relative to the compound of formula (II), preferably between 0.01 and 0.2 molar equivalents.

The depolymerization reaction can be carried out in the absence of a solvent. However, it can be also carried out in the presence of a solvent, and in this case such a solvent could be a saturated or aromatic hydrocarbon having a boiling point above 250° C., e.g. the ones known also under the ESSO's tradenames Marcol® or Primol® or the Hüs's tradename Marlotherm®.

The temperature at which the invention's depolymerization can be carried out is comprised between 80° C. and 220° C., more preferably in the range of between 120° C. and 190° C. Of course, a person skilled in the art is also able to select the preferred temperature as a function of the melting and boiling point of the starting and/or final products as well as the desired time of reaction or conversion.

In some cases, it can be convenient to carry out the invention's process under reduced pressures conditions, such as under pressures comprised between 0.1 and 1000 mbar, preferably between 0.5 and 100 mbar.

EXAMPLES

The invention will now be described in further detail by way of the following examples, wherein the temperatures are indicated in degrees centigrade and the abbreviations have the usual meaning in the art.

All the procedures described hereafter have been carried out under an inert atmosphere unless stated otherwise. All substrates and solvents were distilled from appropriate drying agents under Ar. NMR spectra were recorded on a Bruker AM-400 (¹H at 400.1 MHz) spectrometer and normally measured at 300 K, in CDCl₃ unless indicated otherwise. Chemical shifts are listed in ppm.

Example 1 Preparation of the Oligomeric Product

The oligomeric compound (II) can be prepared according to any standard methods well known by a person skilled in the art. E.g., 1-(3′,3′-Dimethyl-1′-cyclohexyl)-1-ethanol was reacted with isobutylene oxide in the presence of BF₃ as catalyst, under condition of excess of the starting alcohol. The reaction leads to a mixture of products of mono- and di-addition of the epoxide according to the following scheme:

The oligomeric product 1 is easily recovered from the residual material of the fractional distillation of the compound 2 and purified by flash distillation.

Depolymerization of the Oligomeric Product 1:

A 250 ml laboratory reactor equipped with a short packed column, a reflux condenser and a −80° C. cooled trap, was charged with 100 g of the oligomeric product 1 (72% purity) in the presence of 4 g of zirconium tetrapropoxide (70% in propanol). The mixture is progressively heated to 150° C. under vacuum (20 mbar). The pressure is progressively reduced to 10 mbar and the reactor temperature is allowed to increase to 170° C. and then the reaction is left running for 16 hours. During this time, the monomeric compound 2 is distilled into a flask while the volatile compounds (mainly propanol and methallyl alcohol) are collected in the cooled trap.

The distillate thus obtained contains mainly: alcohol 2: 76%; starting alcohol 3: 2.7%; oligomeric compound 1: 11%.

The fractional distillation of the above distillate affords 42 g of the pure alcohol 2 (diastereoisomeric mixture) corresponding to 55% mol yield.

¹H-NMR: 0.86 (s, 3H); 0.90 (s, 3H); 1.05 (d, 3H); 1.13 (s, 3H); 1.15 (s, 3H); 0.7-1.9 (m, 9H); 3.30 (s, 2H); 3.35 (m, 1H)

GC-MS 2a: 228 (M⁺., 0); 197 (10); 139 (96); 123 (18); 117 (27); 97 (25); 83 (96); 73 (100); 69 (35); 55 (42); 41 (25)

GC-MS 2b: 228 (M⁺., 0); 197 (10); 139 (99); 123 (18); 117 (31); 97 (24); 83 (100); 73 (99); 69 (35); 55 (50); 41 (29)

Example 2 Depolymerization of the Oligomeric Product 1 with Various Catalysts (General Procedure)

A 250 ml laboratory reactor equipped with a short packed column, a reflux condenser and a −80° C. cooled trap, was charged with 100 g of the oligomeric product 1 (prepared according to the above procedure, 72% purity) in the presence of the catalyst. The mixture is progressively heated to 150° C. under vacuum (20 mbar). The pressure is progressively reduced to 10 mbar and the reactor temperature is allowed to increase to 165° C. and then the reaction is left running for 4-5 h hours. During this time, the monomeric compound 2 is distilled into a flask while the volatile compounds (mainly propanol and methallyl to alcohol) are collected in the cooled trap.

The distillate thus obtained is fractionated and the alcohol 2 is isolated as the pure product. The following table outlines the tested catalysts and the corresponding results.

Mol Distillate Alcohol 2 Catalyst equivalent weight % Mol yield % Zr(OPr)₄ (Example 1) 0.035 44.6 g 69%   56% Ti(O^(i)Pr)₄ 0.035 25.4 g 60% 27.8% Zr(acac)₄ 0.035 22.8 g 45% 18.7% Al(O^(t)Bu)₃ 0.035   51 g 63% 58.7% Al(O^(sec)Bu)₃ 0.035 33.6 g 33% 20.3% Al(O^(i)Pr)₃ 0.035 32.4 g 38% 22.5% 

1. A process for producing a compound of formula (I):

wherein z represents 1 or 0, and each R¹, independently from each other, represents a hydrogen atom or a methyl or ethyl group, or the two R¹ taken together represent a (CH₂)_(m) group, m representing 3, 4, or 5; each R², independently from each other, represents a hydrogen atom or a methyl or ethyl group, or the two R² taken together represent a (CH₂)_(m) group, m representing 3, 4, or 5; and R³ represents a phenyl group optionally substituted, a saturated or unsaturated C₅-C₆ cyclic hydrocarbon moiety optionally substituted, or a CH(R⁴)₂ or R⁴CH═CR⁴ moiety, R⁴ representing a C₁-C₆ alkyl or alkenyl group optionally substituted; and the substituents of said R³ group are one, two or three C₁-C₃ alkyl, alkenyl or alkoxy groups; wherein the process comprises reacting the corresponding compound of formula (II):

wherein z, R¹, R² and R³ are defined as in formula (I) and x represents an integer comprised between 2 and 10; with at least one metal compound of formula M(R⁵)_((n-2y))(R⁶)_(y), wherein y is 0, 1 or 2; wherein: M represents Zr or Ti, and n is 4, or Al and n is 3, or Mo(O₂)₂ and n is 2; R⁵ represents, independently from each other, a C₁-C₆ alkoxylate group or a C₅-C₈ 1,3-diketonate, and R⁶ represents a 1,2- or 1,3-dialkoxylate or a 1,2-diphenoxylate.
 2. The process according to claim 1, wherein the compounds of formula (I) are those wherein: z represents 1, each R¹, independently from each other, represents a hydrogen atom or a methyl group, or the two R¹ taken together represent a (CH₂)_(m) group, m representing 3 or 4; each R², independently from each other, represents a hydrogen atom or a methyl group, or the two R² taken together represent a (CH₂)_(m) group, m representing 3 or 4; and R³ represents a saturated or unsaturated C₅-C₆ cyclic hydrocarbon moiety optionally substituted, or a CH(R⁴)₂ or R⁴CH═CR⁴ moiety, R⁴ representing a C₁-C₄ alkyl group optionally substituted.
 3. The process according to claim 1, wherein the compounds of formula (I) are those wherein: R³ is 3,3-dimethyl-cyclohexyl, 3,3-dimethyl-cyclohex-1-en-1-yl, 4-methyl-pent-2-en-2-yl, 5-methyl-cyclohex-3-en-1-yl or 2-methyl-cyclohexyl; one or two R¹, per glycol unit of compound (I) or (II), are a methyl group; and at least one R² is a methyl group.
 4. The process according to claim 1, wherein the metal is a compound of formula M(R⁵)_((n-2y))(R⁶)_(y), wherein y is 0 or 1 and: M represents Zr or Ti, and n is 4, or M represents Al and n is 3; with R⁵ representing, independently from each other, a C₁-C₆ alkoxylate group or a C₅-C₈ 1,3-diketonate; and R⁶ representing a 1,2- or 1,3-dialkoxylate.
 5. The process according to claim 4, wherein the metal compound is of formula Ti(R⁵)₄.
 6. The process according to claim 4, wherein the metal compound is of formula Zr(R⁵)₄.
 7. The process according to claim 4, wherein the metal compound is of formula Al(R⁵)₃.
 8. The process according to claim 4, wherein all R⁵ groups represent an alkoxylate group or a 1,3-diketonate group.
 9. The process according to claim 4, wherein the metal compound is added to the reaction mixture in quantities ranging between 0.005 and 1 molar equivalents, relative to the compound of formula (II). 